This is an idea I've had for a while. Many people know the Disney version of The Little Mermaid, but not as many know the original Hans Christian Anderson version. I prefer Anderson's ending where the prince ends up marrying this princess he's been in love with since the little mermaid saved him. The mermaid's sisters go to the sea witch and trade their beautiful hair for a dagger that will let the mermaid turn back into a mermaid and live out the rest of her life that way, but she has to drive the dagger through the prince's heart in order for it to work. The mermaid can't do it and jumps into the ocean where she would turn into sea foam like mermaids do when they die. Instead of turning to foam she finds herself among these beautiful transparent beings called "the daughters of the air" and because of the mermaid's decision to die rather than kill the prince to save herself, she joins the daughters of the air where she would do good deeds to earn an immortal soul (mermaids don't have them) and eventually be allowed into heaven.
So I took the basics of Ariel's design and made her into my version of a daughter of the air and she is flying up in the sky and looking back down lovingly at the ship where the prince married his princess.